The present invention relates to osteosynthesis devices, and more particularly to an improved ring which can be used in combination with a pin or a screw and is intended to maintain one or more fractured bones in compression, such as a bone of the hand or of the foot, and also to a device specially designed for compressing it.
Numerous devices intended to maintain two bones, or two bone fragments of a fractured bone, in compression have been described in the literature. For example, patent FR-A-2,549,650 describes an intra-medullary compression device which comprises a threaded rod bearing two opposite elements which each include disks for anchoring in the medullary cavity of the fractured bone, into which medullary cavity this device is introduced. The devices of this type are not suitable, however, for osteotomy of small bones.
U.S. Pat. No. 3,990,438 describes a fixation device for fractured bones comprising two parts, one of which has cutting threads which anchor in the main fragment of the bone, while the other part includes a thread cooperating with a screw, protruding from the bone, providing for the axial compression. This device cannot be used on bones of small dimension. Furthermore, the removal of the screw is very difficult on account of the osseous incarcerations which occur between the threads of the distal part of the screw and, in addition, the compression is not satisfactory.
Patent EP-A-085,493 describes a compression device comprising a self-tapping screw which engages in a sleeve, and the point of which fixes in the distal bone, as well as a blocking ring which is placed between the body of the screw and the sleeve.
Patent FR-A-2,695,026 describes a screw with fold-back wings integral with the proximal end of the screw, the head of which is hollow and can receive a cylindrical element acting on the free ends of the wings in order to fold them back. The whole arrangement can include an axial channel for the passage of a pin which is used for certain types of fractures.
Patent EP-A-0,209,685 describes a compression device formed by a screw which engages in a peg with a slotted head capable of fixing itself in the bone. This device has the disadvantage of being difficult to withdraw on account of the regrowth of bone which can block the peg.
These known devices are not generally designed for use in the reconstructive surgery of small bones, for example the bones of the foot and of the hand. Moreover, the head of the screw which is traditionally used stands out and forms a projection beyond the surface of the bone, and this entails serious risks of pain and of formation of seats of infection. This difficulty is eliminated in the screw known as the Herbert screw and formed by a headless compression screw, bearing on the two opposite cortical walls of the fractured bone or of the bone fragments, but the positioning of such a screw is a delicate operation.
Finally, it is generally imperative to prepare a very precise drill hole before putting into position the device for maintaining the fractured bone in compression, and this positioning, as well as the compression, are then often awkward to perform under good conditions.
The subject of the present invention is a novel osteosynthesis ring which is particularly designed for small bones, but may also be suitable for bones of large dimension, and which can be used in combination with a pin or a screw, and, where appropriate, an osteosynthesis plate.
Another subject of the invention is a device specially designed for the compression of such an osteosynthesis ring.
The osteosynthesis ring according to the present invention, for maintaining one or more fractured bones in compression, is intended to be used in combination with a pin or a screw, and, where appropriate, an osteosynthesis plate, and is of the type comprising a hollow cylindrical body; it is distinguished by the fact that:
the body of the ring is made of an elastic biocompatible material, PA1 the body of the ring has a channel passing right through it along its axis of revolution and matching the pin, PA1 the body of the ring is equipped on its outer and/or inner part with a means for blocking in translation and/or in rotation, PA1 the proximal part of the body and/or the head of the ring is slotted along at least one diameter in order to form at least two separate parts which are capable of spreading apart from one another.
The means for blocking the osteosynthesis ring according to the invention can be formed by a spiral screw thread on the outer surface of the cylindrical body, cooperating, for example, with a tapped hole made in the osseous part where the ring is to be positioned. In one variant, the outer cylindrical surface is smooth, and the blocking means is formed by at least one flexible tongue, the free end of which will anchor itself in the osseous part or, preferably, in an osteosynthesis plate. In another variant, the blocking is achieved by fixation on the pin itself, and in this case the blocking means is provided on the inner face of the channel passing through the ring.
The osteosynthesis ring according to the invention is preferably formed by a headless screw, but it is possible to use headed screws of various forms.
According to a preferred embodiment, the osteosynthesis ring includes means for temporary attachment to the pin, which means can consist of a circular flange inside the axial channel.
As has been indicated hereinabove, the proximal part of the body and/or the head of the ring is divided into at least two parts by a diametral slot, or by two perpendicular slots, in this case forming a cruciform recess.
This diametral slot can advantageously have a beveled section over part or all of the diameter, facilitating the positioning of the ring, in combination with an apparatus or ancillary device of the type described hereinafter. Moreover, the ring can also include a transverse slot, in a plane perpendicular to the axis of the ring, and passing through the latter along approximately half its diameter, preferably in its distal part, near its central part.
The osteosynthesis ring according to the invention is made of any biocompatible material having satisfactory mechanical properties, and for example of treated steel, stainless steel, steel having a high nitrogen content, an alloy based on titanium, aluminum and vanadium or molybdenum, such as TA6V or TA6M alloys, and in a general manner all the metals corresponding to the standard ISO 5832.
The osteosynthesis ring according to the present invention affords several advantages compared to the conventional devices used in the art.
As in the case of the Herbert screw, it does not form a protrusion at the bone surface, and, moreover, its positioning is made easy because it is guided by the pin. In addition, the same osteosynthesis ring can be used in situations where conventional screws of different sizes would have to be employed.
Furthermore, in the case of an osteosynthesis screw, it is no longer necessary to prepare a drill hole specially designed for the screw, and the positioning of the screw according to the invention is made easier. Consequently, the risks of loss of the reduction of the fracture during the osteosynthesis are greatly reduced.
The production of the ring according to the present invention is simple and relatively inexpensive, since it is not necessary to carry out a delicate operation of perforation for a screw of very small dimension, in contrast to the well known Herbert screw which is poorly adapted to osteosynthesis of the small bones of the foot and of the hand.
The positioning of the ring according to the invention can advantageously be effected using a dynamometric compression device, which greatly limits the risks of excessive traction leading to extraction of the fixation thread of the screw or of the pin from the cortical bone during compression of the fractured bone.
In the case of surgery of the foot, and, especially, of the hand, the ring of the invention, used in the variant of the ring with an external spiral thread, combined with a pin on which it is fixed, permits osteosynthesis of the small bones of the hand to be carried out with greater ease and improved efficacy compared to the conventional techniques, which entail a substantial risk of loss of reduction of the fracture.
In one variant according to the present invention, the ring is associated with a pin including a so-called "distal cancellous" thread and a polygonal cross section, for example hexagonal, permitting the osteosynthesis of fractures of the scaphoid bone, with a possibility of dynamometric compression, avoiding the risks of extraction from the cancellous bone in the distal part.
The invention also extends to an ancillary device specially designed for the compression of an osteosynthesis ring such as has been described hereinabove.
The ancillary device for compression of a fractured bone, using a ring according to the invention, comprises at least two coaxial cylinders which can slide one inside the other along their axis and are connected by a spring, one of the cylinders including means for temporary attachment to the pin or the screw passing through the ring.
The spring is a preset dynamometric spring which can be compressed prior to the positioning of the ring and the compression of the fractured bone.
In a variant designed for a ring fixed on a pin, one of the cylinders comprises, at its free end, means for holding the ring during its positioning, and the other cylinder is provided with a collar or a mandrel for clamping on the pin.
In a second variant designed for a ring fixed on a screw rod associated with an osteosynthesis plate, the ancillary device includes an intermediate cylindrical tube including means for fixing to the plate, for example a screw thread cooperating with a tapped hole provided in the plate.
In a general manner, the ring according to the present invention, combined with a pin and/or a plate, can be employed in all applications where use is made of lost pins, that is to say pins which are left in place after the surgical intervention.
Thus, it can be used in osteosynthesis of fractures of the tibial plateaus, where the characteristics of the ring prevent the pin from migrating. Moreover, the pin can be cut flush with the surface of the bone and no longer protrudes under the skin. This reduces the risks of pain and infection.
The ring of the invention can also be employed in the osteosynthesis of osteochondral fractures of the lower end of the femur, as well as of the astragalus, where the use of the ring in arthroscopy is made easier by the fact that the specially designed ancillary positioning device forms, together with the ring, an assembly which it is easy for the surgeon to manipulate.
In the case of fractures of the wrist, it is possible to use the technique of styloid pinning, and the absence of a protrusion of the pin avoids the risk of tendon rupture on the pin and of infection on the pin, very common in the conventional techniques. Moreover, the lifetime of the osteo-synthesis is distinctly improved by virtue of the good implantation of the pin held by the screw, or the ring, which prevents it from migrating.
The osteosynthesis ring according to the invention can also be used for the reduction of fractures of the neck of the femur, in the same way as in the case of fractures of the scaphoid bone, by giving the twin advantage, compared to the conventional techniques, of great simplicity of positioning and the possibility of dynamometric compression.
In accordance with the present invention, the positioning is carried out in the following manner, more particularly in the case of the variant consisting of a ring with an external screw thread. Once the fracture has been reduced and is being held by a pin, for example a notched pin, the first cortical bone is hollowed out slightly using a suitable instrument, for example a perforated square point. The ring is then mounted on the screwdriver, the effect of which is to spread open the upper parts of the ring by distancing them from one another, and the assembly is engaged on the part of the pin protruding from the bone. The ring is then screwed until it is flush with the surface of the bone, and then the screwdriver is removed.
By virtue of the elasticity of the material used, the upper parts of the ring are drawn together, and the ring is thus blocked on the pin. The form given to the means of attachment of the ring and of the pin makes it possible to obtain a unidirectional or bidirectional blocking in translation, depending on the result which is sought.
The same operation is performed on the opposite cortical bone.
The compression is then carried out on one or other of the two sides, if desired, by means of the ancillary device for dynamometric compression. It then suffices to cut the protruding ends of the pins flush with the rings.
In one variant according to the invention including a pin with a distal threading which can anchor in the opposite cortical bone, this pin is used as a conventional screw, then the ring according to the invention is engaged on the pin, compressed and blocked on the pin as indicated hereinabove.
The pin can have a polygonal cross section and have a male head, in which case a screwdriver with a female head is used.
In the case of a ring according to the invention combined with an osteosynthesis plate, the positioning can be carried out as is described in greater detail hereinafter.